Supported catalysts for converting methane or purified natural gas, preparation thereof, and process for preparation of ethylene using said catalysts

ABSTRACT

Supported catalysts of the following formula (I) for preparing ethylene by conversion of methane or purified natural gas and preparation thereof, and process for preparation of ethylene by direct conversion of methane or purified natural gas using said catalysts: 
     
         Ma&#39;/S                                                      formula (I) 
    
     (wherein, M is a compound selected from the group of RuCl 2  (PPh 3 ) 3 , RuCl 2  (CO) 2  (PPh 3 ) 2 , Ru 3  (CO) 12 , RhCl(CO)(PPh 3 ) 2 , IrCl(CO)(PPh 3 ) 2 , Pd(PPh 3 ) 4 , Pt(PPh 3 ) 4 , RuCl 3  ·xH 2  O, RhCl 3  ·xH 2  O, IrCl 3  ·xH 2  O, PdCl 2  ·xH 2  O, H 2  PtCl 6  ·xH 2  O, S is an inorganic carrier selected from α-Al 2  O 3 , γ-Al 2  O 3 , SiO 2 , SiO 2  --Al 2  O 3 , Y-zeolite, MgO and TiO 2 , a&#39; is weight percentage of metal in catalyst, ranging from 0.25 to 5 wt %.)

FIELD OF THE INVENTION

The present invention relates to supported catalysts of the following formular (I) for producing ethylene which is used in basic reactions including polymerization, copolymerization and polycondensation reaction in the field of petrochemical industry and fine chemical industry, and preparation thereof.

    Ma'/S                                                      formula (I)

Further, the present invention is to provide a new process for preparation of ethylene by converting directly methane or purified natural gas, in the presence of the above catalyst with nitrogen, at a temperature of about 670° to 850° C., preferably in the range of 710° to 810° C., which is distinctly lower reaction temperature relative to that of conventional synthesis of hydrocarbon(s) by dehydrogenation. By this process, ethylene is obtained in short time, with high yield, and without by-product such as CO, CO₂, contrary to oxidative coupling reaction where oxygen is introduced.

In Ma'/S of above mentioned general formular (I), M is a compound selected from the group of RuCl₂ (PPh₃)₃, RuCl₂ (CO)₂ (PPh₃)₂, Ru₃ (CO)₁₂, RhCl(CO)(PPh₃)₂, IrCl(CO)(PPh₃)₂, Pd(PPh₃)₄, Pt(PPh₃)₄, RuCl₃ ·xH₂ O, RhCl₃ ·xH₂ O, IrCl₃ ·xH₂ O, PdCl₂ ·xH₂ O, wherein x is 3-10, H₂ PtCl₆ ·xH₂ O, S is an inorganic carrier selected from α-Al₂ O₃, γ-Al₂ O₃, SiO₂, SiO₂ --Al₂ O₃, Y-zeolite, MgO and TiO₂, a' is weight percentage of metal in catalyst, ranging from 0.25 to 5 wt %.

BACKGROUND ART

Few of literatures and patents about the catalyst which can be used to produce ethylene by direct conversion of methane is disclosed; moreover, it is different in technical field from present invention. By conventional processes, large amounts of by-product such as carbon dioxide are produced, separation and removal thereof is difficult and environmental pollution is likely to be caused. Also, synthesis of hydrocarbon(s) by conventional dehydrogenation is conducted at relatively high temperature of about 1500° to 1550° C. through thermal or electric cracking reaction to cause some problems such as necessity of supply of high energy, expense of high temperature equipment (plan) as well as enormous loss of thermal energy expense, particulary severe corrosion of reactor.

As prior art describing synthesis of hydrocarbon by oxidative coupling or dehydrogenation reaction, there are U.S. Pat. Nos. 5,066,629, 5,068,486 and 5,118,654, Canadian patent no. 2016675 and Japanese patent nos. 04352730, 04368342.

SUMMARY OF THE INVENTION

Until now, new catalyst being able to conduct conversion reaction not at so (ultra) high temperature as that of process for synthesis of hydrocarbons by dehydrogenation but at distinctly lower (mid•low) temperature, and new process for producing said catalyst, and new process for conversion into ethylene using said catalyst have always been expected.

To meet the expectations above, as the result of study for years, the inventors completed development of a new catalyst, preparation thereof, and a simple process for obtaining ethylene in short time, with high yield and with trace amounts of impurities, by converting methane or purified natural gas in the presence of said catalyst at distinctly lower temperature compared to that of process for synthesis of hydrocarbon by dehydrogenation or oxidative coupling reaction; thus direct conversion of methane, being carried out at distinctly low temperature, causes to save enormous amount of thermal energy cost that was needed in synthesis reaction of hydrocarbon(s) by dehydrogenation or oxidative coupling reaction, and is sufficiently efficient to environmental pollution problems through reduced amounts of impurities, namely CO₂.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described in further detail with reference to Examples.

First, new desirable catalyst is produced by supporting organic transition metal compound on inorganic carriers, i.e., by supporting various metal cluster compound and organic metal complex on inorganic carriers.

In this method, process for synthesis and purification of catalyst is much easier than that in other processes.

Through development of this catalyst, reaction conditions such as reaction temperature, reaction pressure are mitigated considerably and ethylene is produced with high yield.

Further, due to development of process using catalyst of the present invention, the process for preparation of ethylene is simplified, as a result, productivity is enhanced.

The present invention is described in detail as follows.

In the present invention, by developing a new process where methane or purified natural gas is converted directly to ethylene, which is different from synthesis reaction of hydrocarbon by dehydrogenation or oxidative coupling reaction, overall process is simplified, further, reaction temperature is lowered to a temperature of about 670° to 850° C., preferably in the range of 710° to 810° C., and amounts of impurities such as carbon dioxide are greatly reduced.

In the present invention, by using RuCl₂ (PPh₃)₃, RuCl₂ (CO)₂ (PPh₃)₂, RhCl(CO)(PPh₃)₂ catalyst, ethylene is produced with high yield at a temperature of about 810° C. At this time, conversion rate is maintained in the range of about 7.5 to 8.3% and through continuous recirculation of raw material introduced, conversion rate is maximized.

That is to say, through solid surface reaction using heterogeneous catalyst, reaction conditions such as reaction temerature and pressure are considerably mitigated, at the same time, reaction equipment is simplified.

Process for preparing supported catalyst of the present invention is as follows.

Metal cluster (compound) and organic metal complex are dissolved in mixed solvent such as dichloromethane and acetone, etc.

Then, inorganic carrier is added to this solution, and metal cluster (compound) and organic metal complex are immersed into inorganic carrier by stirring at about 20° to 200° C., then dried in vacuum drier to prepare catalyst.

Inorganic carriers used here are α-Al₂ O₃, γ-Al₂ O₃, SiO₂, SiO₂ --Al₂ O₃, Y-zeolite, MgO and TiO₂.

And metal cluster(compound) and organic metal complex compounds used are RuCl₂ (PPh₃)₃, RuCl₂ (CO)₂ (PPh₃)₂, Ru₃ (CO)₁₂, RhCl(CO)(PPh₃)₂, IrCl(CO)(PPh₃)₂, Pd(PPh₃)₄, Pt(PPh₃)₄, RuCl₃ ·xH₂ O, RhCl₃ ·xH₂ O, IrCl₃ ·xH₂ O, PdCl₂ ·xH₂ O, H₂ PtCl₆ ·xH₂ O.

According to the experiments of the present invention, the optimum inorganic carriers for preparation of ethylene are α-Al₂ O₃ and MgO, and metal of VIII series are Ru, Rh.

Reaction conditions in the presence of new catalyst of the present invention are as follows.

Dilution ratio of nitrogen to methane or purified natural gas is 1 to 6, preferably 1 to 3, based on methane.

Reaction temperature is about 670° to 850° C., preferably in the range of 710° to 810° C.

Concentration of catalyst is below 5 wt %, prefarably 1 to 3 wt %.

Space velocity of source gas is about 75 to 1200 hr⁻¹, prefarably in the range of 150 to 600 hr⁻¹.

Reaction pressure is usually about 1 to 5 atm, preferably normal pressure.

Conversion rate of methane or purified natural gas, and yield and selectivity of ethylene are defined as follows. ##EQU1##

Reactants and products are analyzed by gas chromatograph.

Examples 1 to 8 relate to new catalyst and process for preparation thereof, Exmaples 9 to 31 relate to new process for producing ethylene by conversion reaction of methane or purified natural gas in the presence of new catalyst of the present invention.

EXAMPLE 1

α-Al₂ O₃ 4.39 g, RuCl₂ (PPh₃)₃ 0.85 g (0.886 mmol) are added to mixed solvent consisting of 20 ml of dichloromethane and 10 ml of acetone. This suspension is stirred for about 30 minutes at a temperature of around 40° C., and evaporated to dryness by distillation under reduced pressure, then dried in vacuum drier for about 20 hours to prepare RuCl₂ (PPh₃)₃ /α-Al₂ O₃ catalyst.

EXAMPLE 2

RuCl₂ (CO)₂ (PPh₃)₂ 0.56 g (0.744 mmol) is added to mixed solvent consisting of 40 ml of dichloromethane and 10 ml of acetone and dissolved, then α-Al₂ O₃ 3.68 g is added thereto. This suspension is stirred for about 30 minutes at a temperature of around 40° C. and solvent is evaporated by distillation under reduced pressure. Then residue obtained is dried in vacuum drier for about 20 hours to prepare RuCl₂ (CO)₂ (PPh₃)₂ /α-Al₂ O₃ catalyst.

EXAMPLE 3

α-Al₂ O₃ 3.95 g, Ru₃ (CO)₁₂ 0.17 g (0.266 mmol) are added to mixted solvent consisting of 10 ml of dichloromethane and 100 ml of acetone and dissolved.

This suspension is stirred for about 30 minutes at a temperature of around 40° C. and solvent is evaporated by distillation under reduced pressure.

Residue obtained is dried in vacuum drier for about 20 hours to prepare Ru₃ (CO)₁₂ /α-Al₂ O₃ catalyst.

EXAMPLE 4

α-Al₂ O₃ 3.28 g, RhCl(CO)(PPh₃)₂ 0.45 g (0.652 mmol) are added to mixted solvent consisting of 40 ml of dichloromethane and 20 ml of acetone and dissolved.

This suspension is stirred for about 30 minutes at a temperature of around 40° C. and solvent is evaporated by distillation under reduced pressure.

Residue obtained is dried in vacuum drier for about 20 hours to prepare RhCl(CO)(PPh₃)₂ /α-Al₂ O₃ catalyst.

EXAMPLE 5

α-Al₂ O₃ 3.14 g, IrCl(CO)(PPh₃)₂ 0.26 g (0.333 mmol) are added to mixed solvent consisting of 60 ml of dichloromethane and 10 ml of acetone and dissolved.

This suspension is stirred for about 30 minutes at a temperature of around 40° C. and solvent is evaporated by distillation under reduced pressure.

Residue obtained is dried in vacuum drier for about 20 hours to prepare IrCl(CO)(PPh₃)₂ /α-Al₂ O₃ catalyst.

EXAMPLE 6

α-Al₂ O₃ 3.79 g, Pd(PPh₃)₄ 0.84 g (0.727 mmol) are added to mixted solvent consisting of 20 ml of dichloromethane and 10 ml of acetone and dissolved.

This suspension is stirred for about 30 minutes at a temperature of around 40° C. and solvent is evaporated by distillation under reduced pressure.

Residue obtained is dried in vacuum drier for about 20 hours to prepare Pd(PPh₃)₄ /α-Al₂ O₃ catalyst.

EXAMPLE 7

α-Al₂ O₃ 4.45 g, Pt(PPh₃)₄ 0.58 g (0.466 mmol) are added to mixted solvent consisting of 20 ml of dichloromethane and 10 ml of acetone and dissolved.

This suspension is stirred for about 30 minutes at a temperature of around 40° C. and solvent is evaporated by distillation under reduced pressure.

Residue obtained is dried in vacuum drier for about 20 hours to prepare Pt(PPh₃)₄ /α-Al₂ O₃ catalyst.

EXAMPLE 8

γ-Al₂ O₃ 4.39g, RuCl₂ (PPh₃)₃ 0.85 g (0.886 mmol) are added to mixed solvent consisting of 20 ml of dichloromethane and 10 ml of acetone and stirred for about 30 minutes at a temperature of around 40° C. This suspension is evaporated to dryness by distillation under reduced pressure, then dried in vacuum drier for about 20 hours to prepare RuCl₂ (PPh₃)₃ /γ-Al₂ O₃ catalyst.

EXAMPLE 9

Except using SiO₂ 4.39 g as inorganic carrier, Example 8 is repeated to prepare RuCl₂ (PPh₃)₃ /SiO₂ catalyst.

EXAMPLE 10

Except using SiO₂ --Al₂ O₃ 4.39 g as inorganic carrier, Example 8 is repeated to prepare RuCl₂ (PPh₃)₃ /SiO₂ --Al₂ O₃ catalyst.

EXAMPLE 11

Except using Y-zeolite 4.39 g as inorganic carrier, Example 8 is repeated to prepare RuCl₂ (PPh₃)₃ /Y-zeolite catalyst.

EXAMPLE 12

Except using MgO 4.39 g as inorganic carrier, Example 8 is repeated to prepare RuCl₂ (PPh₃)₃ /MgO catalyst.

EXAMPLE 13

Except using TiO₂ 4.39 g as inorganic carrier, Example 8 is repeated to prepare RuCl₂ (PPh₃)₃ /TiO₂ catalyst.

EXAMPLE 14

α-Al₂ O₃ 5.01 g, RuCl₃ ·xH₂ O 0.21 g (1.012 mmol) are added to mixed solvent consisting of 20 ml of dichloromethane and 10 ml of acetone and stirred for about 30 minutes at a temperature of around 40° C.

This suspension is evaporated to dryness by distillation under reduced pressure, then dried in vacuum drier for about 20 hours to prepare RuCl₃ ·xH₂ O/α-Al₂ O₃ catalyst.

EXAMPLE 15

Except that α-Al₂ O₃ 3.62 g, RhCl₃ ·xH₂ O 0.15 g (0.717 mmol) are added to mixed solvent consisting of 10 ml of dichloromethane and 20 ml of ethanol, Example 14 is repeated to prepare RhCl₃ ·xH₂ O/α-Al₂ O₃ catalyst.

EXAMPLE 16

Except α-Al₂ O₃ 3.79 g, IrCl₃ ·xH₂ O 0.12 g (0.402 mmol) are added to 20 ml of N,N-Dimethylformamide, and stirred at a temperature of around 150° C., Example 14 is repeated to prepare IrCl₃ ·xH₂ O/α-Al₂ O₃ catalyst.

EXAMPLE 17

α-Al₂ O₃ 3.53 g, PdCl₂ ·xH₂ O 0.12 g (0.677 mmol) are dissolved in mixed aqueous sollution of distilled water 30 ml and 35% conc. HCl 1 ml, then stirred for about 30 minutes at around 100° C.

This suspension is evaporated to dryness by distillation under reduced pressure, then dried in vacuum drier for about 20 hours to prepare PdCl₂ ·xH₂ O/α-Al₂ O₃ catalyst.

EXAMPLE 18

Except using H₂ PtCl₆ ·xH₂ O 0.15 g (0.366 mmol), Example 14 is repeated to prepare H₂ PtCl₆ ·xH₂ O/α-Al₂ O₃ catalyst.

EXAMPLE 19

Methane (or purified natural gas) and nitrogen are introduced each at the flow rate of about 10 ml/min into continuous stationary phase flow reactor (inner diameter: 0.70 cm; length: 40 cm; stuff: stainless steel 316) in the presence of the catalyst prepared in Example 1. Products are obtained by continuous reaction under about 1 atm at each reaction temperature which is given in following Table 1 and the results of analysis of them by gas chromatography is as following Table 1 (from this example to Example 31, raw material is continuously reintroduced to convesion reaction).

Below mentioned * mark represents reaction is conducted at surrounding temperature based on given value.

                  TABLE 1     ______________________________________     Reaction         Yield         Selectivity     Temp.  Conversion                      (%)           (%)     *(°C.)            (%)       Ethylene Ethane Ethylene                                             Ethane     ______________________________________     710    about 2.0 about 1.1                               about 0.9                                      about 55.0                                             about 45.0     730    about 2.9 about 2.1                               about 0.8                                      about 72.4                                             about 27.6     750    about 4.4 about 3.6                               about 0.8                                      about 81.8                                             about 18.2     770    about 5.4 about 4.8                               about 0.6                                      about 88.9                                             about 11.1     790    about 6.6 about 6.0                               about 0.6                                      about 90.9                                             about 9.1     810    about 7.5 about 6.8                               about 0.7                                      about 90.7                                             about 9.3     ______________________________________

EXAMPLE 20

Except using RuCl₂ (CO)₂ (PPh₃)₂ /α-Al₂ O₃ as catalyst, Example 19 is repeated and the distribution of resultant products is as following Table 2.

                  TABLE 2     ______________________________________     Reaction         Yield         Selectivity     Temp.  Conversion                      (%)           (%)     *(°C.)            (%)       Ethylene Ethane Ethylene                                             Ethane     ______________________________________     710    about 2.1 about 1.2                               about 0.9                                      about 57.1                                             about 42.9     730    about 3.1 about 2.1                               about 1.0                                      about 67.7                                             about 32.3     750    about 4.5 about 3.7                               about 0.8                                      about 82.2                                             about 17.8     770    about 5.6 about 4.9                               about 0.7                                      about 87.5                                             about 12.5     790    about 6.5 about 5.9                               about 0.6                                      about 90.8                                             about 9.2     810    about 7.9 about 7.3                               about 0.6                                      about 92.4                                             about 7.6     ______________________________________

EXAMPLE 21

Except using Ru₃ (CO)₁₂ /α-Al₂ O₃ as catalyst, Example 19 is repeated and the distribution of resultant products is as following Table 3.

                  TABLE 3     ______________________________________     Reaction         Yield         Selectivity     Temp.  Conversion                      (%)           (%)     *(°C.)            (%)       Ethylene Ethane Ethylene                                             Ethane     ______________________________________     710    about 1.4 about 0.5                               about 0.9                                      about 35.7                                             about 64.3     730    about 2.6 about 1.6                               about 1.0                                      about 61.5                                             about 38.5     750    about 3.8 about 2.8                               about 1.0                                      about 73.7                                             about 26.3     770    about 4.6 about 3.7                               about 0.9                                      about 80.4                                             about 19.6     790    about 6.4 about 5.1                               about 1.3                                      about 79.7                                             about 20.3     810    about 7.3 about 5.9                               about 1.4                                      about 80.8                                             about 19.2     ______________________________________

EXAMPLE 22

Except using RhCl(CO)(PPh₃)₂ /α-Al₂ O₃ as catalyst, Example 19 is repeated and the distribution of resultant products is as following Table 4.

                  TABLE 4     ______________________________________     Reaction         Yield         Selectivity     Temp.  Conversion                      (%)           (%)     *(°C.)            (%)       Ethylene Ethane Ethylene                                             Ethane     ______________________________________     710    about 2.2 about 1.2                               about 1.0                                      about 54.5                                             about 45.5     730    about 2.6 about 1.8                               about 0.8                                      about 69.2                                             about 30.8     750    about 4.4 about 3.4                               about 1.0                                      about 77.3                                             about 22.7     770    about 5.5 about 4.7                               about 0.8                                      about 85.5                                             about 14.5     790    about 6.7 about 6.0                               about 0.7                                      about 89.6                                             about 10.4     810    about 8.3 about 7.6                               about 0.7                                      about 91.6                                             about 8.4     ______________________________________

EXAMPLE 23

Except using IrCl(CO)(PPh₃)₂ /α-Al₂ O₃ as catalyst, Example 19 is repeated and the distribution of resultant products is as following Table 5.

                  TABLE 5     ______________________________________     Reaction         Yield         Selectivity     Temp.  Conversion                      (%)           (%)     *(°C.)            (%)       Ethylene Ethane Ethylene                                             Ethane     ______________________________________     710    about 1.3 about 0.6                               about 0.7                                      about 46.2                                             about 53.8     730    about 2.5 about 1.8                               about 0.7                                      about 72.0                                             about 28.0     750    about 3.6 about 2.6                               about 1.0                                      about 72.2                                             about 27.8     770    about 5.1 about 4.3                               about 0.8                                      about 84.3                                             about 15.7     790    about 6.1 about 5.4                               about 0.7                                      about 88.5                                             about 11.5     810    about 7.3 about 6.7                               about 0.6                                      about 91.8                                             about 8.2     ______________________________________

EXAMPLE 24

Except using Pd(PPh₃)₄ /α-Al₂ O₃ as catalyst, Example 19 is repeated and the distribution of resultant products is as following Table 6.

                  TABLE 6     ______________________________________     Reaction         Yield         Selectivity     Temp.  Conversion                      (%)           (%)     *(°C.)            (%)       Ethylene Ethane Ethylene                                             Ethane     ______________________________________     710    about 1.1 about 0.5                               about 0.6                                      about 45.5                                             about 54.5     730    about 1.5 about 0.9                               about 0.6                                      about 60.0                                             about 40.0     750    about 3.6 about 2.6                               about 1.0                                      about 72.2                                             about 27.8     770    about 5.2 about 4.1                               about 1.1                                      about 78.8                                             about 21.2     790    about 5.9 about 5.1                               about 0.8                                      about 86.4                                             about 13.6     810    about 7.2 about 6.7                               about 0.6                                      about 93.1                                             about 6.9     ______________________________________

EXAMPLE 25

Except using Pt(PPh₃)₄ /α-Al₂ O₃ as catalyst, Example 19 is repeated and the distribution of resultant products is as following Table 7.

                  TABLE 7     ______________________________________     Reaction         Yield         Selectivity     Temp.  Conversion                      (%)           (%)     *(°C.)            (%)       Ethylene Ethane Ethylene                                             Ethane     ______________________________________     710    about 1.2 about 0.6                               about 0.6                                      about 50.0                                             about 50.0     730    about 1.8 about 1.1                               about 0.7                                      about 61.1                                             about 38.9     750    about 3.0 about 2.3                               about 0.7                                      about 76.7                                             about 23.3     770    about 4.6 about 3.8                               about 0.8                                      about 82.6                                             about 17.4     790    about 5.8 about 5.1                               about 0.7                                      about 87.9                                             about 12.1     810    about 7.3 about 6.6                               about 0.7                                      about 90.4                                             about 9.6     ______________________________________

EXAMPLE 26

Except using RuCl₂ (PPh₃)₃ /γ-Al₂ O₃ as catalyst, Example 19 is repeated and the distribution of resultant products is as following Table 8.

                  TABLE 8     ______________________________________     Reaction         Yield         Selectivity     Temp.  Conversion                      (%)           (%)     *(°C.)            (%)       Ethylene Ethane Ethylene                                             Ethane     ______________________________________     710    about 1.4 about 1.0                               about 0.4                                      about 71.4                                             about 28.6     730    about 1.8 about 1.3                               about 0.5                                      about 72.2                                             about 27.8     750    about 2.3 about 1.7                               about 0.6                                      about 73.9                                             about 26.1     770    about 2.8 about 2.1                               about 0.7                                      about 75.0                                             about 25.0     790    about 4.7 about 3.9                               about 0.8                                      about 83.0                                             about 17.0     ______________________________________

EXAMPLE 27

Except using RuCl₂ (PPh₃)₃ /SiO₂ --Al₂ O₃ as catalyst, Example 19 is repeated and the distribution of resultant products is as following Table 9.

                  TABLE 9     ______________________________________     Reaction            Conver-  Yield         Selectivity     Temp.  sion     (%)           (%)     *(°C.)            (%)      Ethylene Ethane Ethylene                                             Ethane     ______________________________________     710    about 1.3                     about 1.3                              about 0.0                                     about 100.0                                             about 0.0     730    about 1.8                     about 1.2                              about 0.6                                     about 66.7                                             about 33.3     750    about 3.2                     about 2.2                              about 1.0                                     about 68.8                                             about 31.2     770    about 4.1                     about 3.1                              about 1.0                                     about 75.6                                             about 24.4     790    about 5.7                     about 4.9                              about 0.8                                     about 86.0                                             about 14.0     ______________________________________

EXAMPLE 28

Except using RuCl₂ (PPh₃)₃ /Y-zeolite as catalyst, Example 19 is repeated and the distribution of resultant products is as following Table 10.

                  TABLE 10     ______________________________________     Temp.            Yield         Selectivity     Reaction            Conversion                      (%)           (%)     *(°C.)            (%)       Ethylene Ethane Ethylene                                             Ethane     ______________________________________     710    about 1.9 about 1.4                               about 0.5                                      about 73.7                                             about 26.3     730    about 2.6 about 1.9                               about 0.7                                      about 73.1                                             about 26.9     750    about 4.0 about 3.0                               about 1.0                                      about 75.0                                             about 25.0     770    about 4.3 about 3.5                               about 0.8                                      about 81.4                                             about 18.6     790    about 4.8 about 4.0                               about 0.8                                      about 83.3                                             about 16.7     ______________________________________

EXAMPLE 29

Except using RuCl₂ (PPh₃)₃ /MgO as catalyst, Example 19 is repeated and the distribution of resultant products is as following Table 11.

                  TABLE 11     ______________________________________     Reaction         Yield         Selectivity     Temp.  Conversion                      (%)           (%)     *(°C.)            (%)       Ethylene Ethane Ethylene                                             Ethane     ______________________________________     710    about 2.4 about 1.3                               about 1.1                                      about 54.2                                             about 45.8     730    about 3.2 about 2.0                               about 1.2                                      about 62.5                                             about 37.5     750    about 4.1 about 3.1                               about 1.0                                      about 75.6                                             about 24.4     770    about 4.5 about 3.6                               about 0.9                                      about 80.0                                             about 20.0     790    about 5.9 about 5.1                               about 0.8                                      about 86.4                                             about 13.6     ______________________________________

EXAMPLE 30

Except using RuCl₃ ·xH₂ O/α-Al₂ O₃ as catalyst, Example 19 is repeated and the distribution of resultant products is as following Table 12.

                  TABLE 12     ______________________________________     Reaction            Conver-  Yield         Selectivity     Temp.  sion     (%)           (%)     *(°C.)            (%)      Ethylene Ethane Ethylene                                            Ethane     ______________________________________     710    about 0.0                     about 0.0                              about 0.0                                     about 0.0                                            about 0.0     730    about 0.3                     about 0.0                              about 0.3                                     about 0.0                                            about 100.0     750    about 1.0                     about 0.2                              about 0.8                                     about 20.0                                            about 80.0     770    about 1.8                     about 0.8                              about 1.0                                     about 44.4                                            about 55.6     790    about 2.7                     about 1.7                              about 1.0                                     about 63.0                                            about 37.0     ______________________________________

EXAMPLE 31

Except using RhCl₃ ·xH₂ O/α-Al₂ O₃ as catalyst, Example 19 is repeated and the distribution of resultant products is as following Table 13.

                  TABLE 13     ______________________________________     Reaction            Conver-  Yield         Selectivity     Temp.  sion     (%)           (%)     *(°C.)            (%)      Ethylene Ethane Ethylene                                            Ethane     ______________________________________     710    about 0.0                     about 0.0                              about 0.0                                     about 0.0                                            about 0.0     730    about 0.0                     about 0.0                              about 0.0                                     about 0.0                                            about 0.0     750    about 0.4                     about 0.0                              about 0.4                                     about 0.0                                            about 100.0     770    about 1.7                     about 0.9                              about 0.8                                     about 52.9                                            about 47.1     790    about 3.3                     about 2.4                              about 0.9                                     about 72.7                                            about 27.3     ______________________________________ 

What is claimed is:
 1. A catalyst for preparing ethylene by conversion of methane or purified natural gas; said catalyst having the general formula

    Ma'/S                                                      (I)

wherein, M is a compound selected from the group consisting of RuCl₂ (PPh₃)₃, RuCl₂ (CO)₂ (PPh₃)₂, Ru₃ (CO)₁₂, RhCl(CO)(PPh₃)₂, IrCl(CO)(PPh₃)₂, Pd(PPh₃)₄, Pt(PPh₃)₄, RuCl₃ ·xH₂ O, RhCl₃ ·xH₂ O, and PdCl₂ ·xH₂ C, x being from 3-10; S is an inorganic carrier selected from the group consisting of α-Al₂ O₃, γ-Al₂ O₃, SiO₂, SiO₂ --Al₂ O₃, Y-zeolite, MgO and TiO₂ ; and a' is an amount of metal corresponding to 0.25 to 5 wt % of the catalyst; wherein M is supported on the inorganic carrier, S.
 2. The catalyst of claim 1 wherein M is RuCl₂ (PPh₃)₃ and S is α-Al₂ O₃.
 3. The catalyst of claim 1 wherein M is RuCl₂ (CO)₂ (PPh₃)₂ and S is α-Al₂ O₃.
 4. The catalyst of claim 1 wherein M is Ru₃ (CO)₁₂ and S is α-Al₂ O₃.
 5. The catalyst of claim 1 wherein M is RhCl(CO)(PPh₃)₂ and S is α-Al₂ O₃.
 6. The catalyst of claim 1 wherein M is IrCl(CO)(PPh₃)₂ and S is α-Al₂ O₃.
 7. The catalyst of claim 1 wherein M is Pd(PPh₃)₄ and S is α-Al₂ O₃.
 8. The catalyst of claim 1 wherein M is Pt(PPh₃)₄ and S is α-Al₂ O₃.
 9. The catalyst of claim 1 wherein M is RuCl₂ (PPh₃)₃ and S is γ-Al₂ O₃.
 10. The catalyst of claim 1 wherein M is RuCl₂ (PPh₃)₃ and S is SiO₂.
 11. The catalyst of claim 1 wherein M is RuCl₂ (PPh₃)₃ and S is SiO₂ --Al₂ O₃.
 12. The catalyst of claim 1 wherein M is RuCl₂ (PPh₃)₃ and S is Y-zeolite.
 13. The catalyst of claim 1 wherein M is RuCl₂ (PPh₃)₃ and S is MgO.
 14. The catalyst of claim 1 wherein M is RuCl₂ (PPh₃)₃ and S is TiO₂.
 15. The catalyst of claim 1 wherein M is RuCl₃ ·xH₂ O and S is α-Al₂ O₃.
 16. The catalyst of claim 1 wherein M is RhCl₃ ·xH₂ O and S is α-Al₂ O₃.
 17. The catalyst of claim 1 wherein M is PdCl₂ ·xH₂ O and S is α-Al₂ O₃.
 18. The catalyst of claim 1 wherein, in the presence of said catalyst, ethylene is prepared by reacting methane or purified natural gas and nitrogen at a temperature of about 670° C. to 850° C., under a pressure of under 1 to 5 atm.
 19. The catalyst of claim 18 wherein the concentration of the catalyst is between 1 to 3 wt %.
 20. A process for preparing the catalyst according to claim 1, which comprises the steps of: (a) adding M and S to a single or mixed solvent of dichloromethane and acetone to obtain a suspension; (b) reflux-stirring the suspension at a temperature of about 30° to 250° C.; (c) then, evaporating the solvent by distillation under reduced pressure; and (d) vacuum drying the residue.
 21. The process according to claim 20, wherein the suspension is reflux-stirred at a temperature of 40° to 150° C. 